proposed VODataService changes

[Doug Tody]

Hi -

If we were to keep things as they are now and fold catalog and schema
as "." delimited items into the table name, then what Pat describes is
probably possible for a DBMS that actually provides both catalogs and
schemas separately (many do not).  It would fall out that way as only
such a DBMS would provide both in the table name.  If however the schema
is specified as a separate metadata item and that is all we have, then
the service model describes only a single SQL catalog per service, and
it is probably not possible to access multiple catalogs unless somehow
the service can resolve a logical schema reference into something which
is fully qualified for the specific DBMS.

In either case merely having "schema" and table may be enough for TAP,
since many DBMSes do not provide more than these two levels (often
only either catalog or schema is provided).  I do think that supporting
logical schemas is important to do somehow or other.  The main reason for
breaking schema out separately might be to allow additional per-schema
metadata to be provided.

	- Doug



On Wed, 21 May 2008, Francois Ochsenbein wrote:

>
> Pat,
>
> >
> >On 2008-5-20 08:07, Francois Ochsenbein wrote:
> >> would be interesting to specify what's the scope of the elements
> >> included in the <join>: can these refer to different catalogs ?
> >>
> >>    <catalog>
> >>      <name>The X survey catalog</name>
> >>      <description>...</description>
> >>      <table>
> >>         <schema>...</schema>
> >>         <name>...</name>
> >>         <description>...</description>
> >>         <column>...</column>
> >>         <column>...</column>
> >>         ...
> >>      </table>
> >>      <function>                      <!-- optional -->
> >>         <schema>...</schema>
> >>         <name>...</name>
> >>         ...
> >>      </function>
> >>      <join>                          <!-- optional -->
> >>         ...
> >>      </join>
> >>    </catalog>
> >>
> >
> >
>
> Pat,
>
> Do you mean it would be legal that a <join> in the Registry can define
> a foreign key which would refer to a column of a table of another catalog --
> in other terms, a foreign key to another data server ?
>
> Cheers, francois
> ================================================================================
> Francois Ochsenbein       ------       Observatoire Astronomique de Strasbourg
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